1. Field of the Invention
The present invention relates to an ATM network system, and in particular to an ATM network system which connects a source (transmitting) terminal equipment to a destination (receiving) terminal equipment through a plurality of ATM communication nodes by the SVC (Switched Virtual Connection) method for establishing or releasing the connection between both of the terminal equipments by a signaling process.
In accordance with a recent development of an ATM network, there have been put into practice not only a network configuration by the PVC (Permanent Virtual Connection) method for establishing a fixed connection between ATM communication nodes prior to the communication but also a network configuration by the SVC method for establishing a connection only for a communication period.
For such an ATM network, a source terminal equipment requires a Quality of Service (QoS) upon establishing a connection, and the network performs a traffic control for assigning resources to guarantee the required QoS. This traffic control is important to efficiently use the network.
2. Description of the Related Art
FIG. 12 illustrates an arrangement of a general ATM network system, in which a source terminal 1 and a destination terminal 2 are mutually connected through ATM communication nodes 3a-3c (hereinafter generally designated by reference numeral 3).
FIG. 13 illustrates an arrangement of a prior art ATM communication node 3, which is composed of a physical interface unit 4 connected to external ATM communication nodes and a SW (switch) control unit 5 connected to the physical interface unit 4.
If the network shown in FIG. 12 is set up by the PVC method, a PVC is set up which preliminarily designates as a parameter a priority level depending on a command input in advance of the communication.
Then, the source terminal 1 transmits a user s information cell, a frame, a datagram or the like to the ATM communication node 3a. 
In the ATM communication node 3a, the user""s information cell is inputted from the physical interface unit 4 to the SW-control unit 5 (see FIG. 13), in which the user""s information cell is subject to a traffic control according to the designated priority level and is transferred from the physical interface unit 4 to the next ATM communication node 3b. Likewise, the user""s information cell is subject to a traffic control according to the designated priority level in the ATM communication nodes 3b, 3c and is transferred to the destination terminal 2.
The service categories set in the ATM network are as follows:
{circle around (1)} CBR service: Constant Bit Rate service
{circle around (2)} VBR service: Variable Bit Rate service
{circle around (3)} ABR service: Available Bit Rate service
It is to be noted that the VBR service includes rt-VBR service (real time-Variable Bit Rate service) and nrt-VBR (non real time-Variable Bit Rate service). It is also to be noted that the UBR service has a connection priority level lower than the other service categories because of soft requirements with regard to the traffic characteristics.
Upon establishing, i.e. setting up a PVC, each of the ATM communication nodes determines whether or not it is possible to accept the connection of the required service category depending on its buffer size, the link capacity, and how the resource of connection is used. If possible, a connection which is assigned a resource such as a buffer or a link band is set up.
FIG. 14 illustrates an arrangement of the SW control unit 5, in which a buffer 51 is composed of a CBR/rt-VBR buffer 51a, an irt-VBR buffer 51b, and a UBR buffer 51c per a service category, the buffers 51a-51c being connected to a readout controller 52.
To the interface unit of the ATM communication node, is given the connections of the aforementioned service categories as multiplexed. The user""s information cell of each of the connections is inputted to the CBR/rt-VBR buffer 51a, the nrt-VBR buffer 51b, or the UBR buffer 51c corresponding to the service category.
The readout controller 52 is provided with an available band on the interface to perform a readout control for the user""s information cell. As a result, the quality of service of the user""s information cell as read out can meet the requirement of the traffic characteristic.
On the other hand, if the network is set up by the PVC method, it is possible to layer the priority levels of the connection by receiving the priority levels as a parameter upon setting up the connection in advance of the communication. For example, by designating the priority levels of the connection with a command input upon setting up a PVC, it is possible to layer the priority levels also for the UBR communication connection.
Including an LAN emulation service integrating the existing LAN into the ATM network, a number of services or applications which enable an LAN system communication through the ATM network are based on the SVC method. For the ATM service category, the UBR service is generally used.
However, if the ATM network is set up by the SVC method, since it is not easy for the user to set the priority levels per each connection, a prior art ATM network system by the SVC method does not layer the priority levels in the UBR communication connection.
It is accordingly an object to provide an ATM network system connecting a source terminal equipment to a destination terminal equipment through a plurality of ATM communication nodes by the SVC method wherein the priority levels for the UBR communication connection can be easily layered.
[1] For the achievement of the above object, in an ATM network system according to the present invention, an ATM communication node adjacent to a source terminal equipment comprises a priority level definition table in which priority levels for an SVC whose service category is the UBR are preset per a physical port, a control unit which transmits a SETUP message including the priority levels when the SVC is set up, and a switch controller for controlling a readout level of a user""s information cell based on the priority levels; each of ATM communication nodes having received the SETUP message comprising a switch controller which controls a readout level of the user""s information cell of the SVC based on the priority levels included in the SETUP message.
Namely, in FIG. 1A, a priority level definition table 8 provided in an ATM communication node 3a (hereinafter occasionally referred to as a source ATM communication node) adjacent to a source terminal equipment is preset with priority levels per a physical port. A control unit (not shown) of the ATM communication node 3a having received a user""s information cell of the UBR service retrieves the definition table 8 to recognize the priority levels from the physical port (accommodation position) which has received the user""s information cell, so that a SETUP message 7b including the priority levels as an information element is transmitted for a communication request.
In FIG. 1A, a repeating ATM communication node 3b determines the priority levels of the UBR service from the information element in the received SETUP message 7b. Then the ATM communication node 3b transfers the received SETUP message 7b as a SETUP message 7c. The same operations will be repeated until an ATM communication node 3c adjacent to a destination terminal equipment receives the SETUP message.
In FIG. 1C, is illustrated an operation example in which a user""s information cell 9 is transferred through the SVC of the UBR service set up between the source terminal 1 and the destination terminal 2.
Switch controllers 52 in the ATM communication nodes 3a-3c control reading out the user""s information cell 9 from cell buffers (not shown) according to the priority levels.
As a result, the priority levels of the SVC with the service category of the UBR service can be layered per a physical port.
[2] In the above invention [1], the ATM communication node adjacent to the source terminal equipment may have a multi-layer processing portion used in MAC address, and the priority level definition table may be set per MAC address instead of physical port.
Namely, in FIG. 1A, the priority level definition table 8 may be preset with the priority levels per MAC address. The ATM communication node 3a having received a frame of the UBR service retrieves, in a multi-layer processing portion (not shown), the definition table 8 to recognize the priority levels corresponding to the source or destination MAC address, so that the SETUP message 7b having the priority levels as an information element can be transmitted.
As a result, the priority levels of the SVC with the service category of the UBR service can be layered per MAC address.
[3] In the above invention [1], the ATM communication node adjacent to the source terminal equipment may have a multi-layer processing portion used in IP address, and the priority level definition table may be set per IP address instead of physical port.
Namely, in FIG. 1A, the priority level definition table 8 may be preset with the priority levels per IP address. The ATM communication node 3a having received a datagram of the UBR service makes reference to the definition table 8 in the multi-layer processing on to recognize the priority levels corresponding to the source or destination IP address, so that the SETUP message 7b having the priority levels as an information element can be transmitted.
As a result, the priority levels of the SVC with the service category of the UBR service can be layered per IP address.
[4] In any one of the above inventions [1]-[3], the SETUP message may be based on a signaling protocol prescribed by the PNNI (Private Network Network Interface), and the priority levels may correspond to predetermined values set in an Extended QoS Parameter which is an information element in the SETUP message.
In FIGS. 1A and 1B, a signaling process between the ATM communication nodes 3a-3c may be carried out by the adoption of signaling protocol prescribed by the PNNI. Predetermined values corresponding to the priority levels may be set for a communication request in the Extended QoS Parameter which is an information element of the SETUP message according to the protocol.
Namely, the Extended QoS Parameter is an information element, which is not terminated in the ATM network system, is related to a transmission quality such as delay or fluctuation, and has an information field the user can freely set.
Therefore, the ATM communication node transmits the SETUP message 7b in which values corresponding to the priority levels are set in the information element. The ATM communication nodes 3b, 3c having received the SETUP message 7b can determine the priority levels of the connection depending on numerical values set in the Extended QoS Parameter.
As a result, by using an in-message information element of the standard protocol, the priority levels can be layered also for the SVC in which a traffic parameter regarding a service guarantee whose service category is the UBR service is not prescribed.
[5] In the above invention [4], the priority levels may be set in an End-to-End Transit Delay which is an information element in the SETUP message instead of the Extended QoS Parameter.
Namely, the End-to-End Transit Delay is an information element, which is not terminated in the ATM network system, is related to a transmission quality such as delay, and has an information field the user can freely set in the same manner as the extended QoS parameter.
Accordingly, in FIGS. 1A and 1B, the signaling process between the ATM communication nodes 3a-3c may be carried out under the signaling protocol prescribed by the PNNI. Predetermined values corresponding to the priority levels may be set for a communication request in End-to-End Transit Delay which is an information element in the SETUP message in the protocol.
The ATM communication nodes 3b, 3c having received the SETUP message determine the priority levels of the connection depending on the numerical values set for the End-to-End Transit Delay.
As a result, by using the in-message information element of the standard protocol, the priority levels can be layered also for the SVC in which a traffic parameter regarding a service guarantee whose service category is the UBR service is not prescribed.
[6] In any one of the above inventions [1]-[3], the priority level definition table may be set by a command input from a setting terminal connected to the ATM communication node adjacent to the source terminal equipment.
Namely, in FIG. 1A, being connected to the source ATM communication node 3a, a setting terminal 6 can easily set and modify the priority level definition table 8.
[7] In any one of the above inventions [1]-[3], the switch controller may have a weighted round robin scheduler which weights a readout of the user""s information cell of the SVC corresponding to the priority levels and sequentially reads out the user""s information cell.
FIG. 2 illustrates an operation example of a cell buffer 51 and the switch controller 52 (see FIG. 1C). The cell buffer 51 is composed of cell buffers 51a-51c, and the switch controller 52 includes a weighted round robin scheduler 54. In FIG. 2A, the user""s information cell is temporality stored in the cell buffers 51a-51c respectively, corresponding to priority levels xe2x80x9chighxe2x80x9d, xe2x80x9cmiddlexe2x80x9d, and xe2x80x9clowxe2x80x9d. The scheduler 54 can read out the user""s information cell in accordance with the weight corresponding to the priority levels from the cell buffers 51a-51c. 
FIG. 2B schematically illustrates the above readout operation. That a readout weight is set according to the priority levels means that the switch controller 52 prepares an available band for the readout control at the rates corresponding to the priority levels for reading out the cell from the cell buffer 51.
As a result, in the available band a valid cell with a lower priority level can be also read out even in the presence of a valid cell with a higher priority level.
[8] In any one of the above inventions [1]-[3], each ATM communication node may further comprise a connection/priority level table in which the priority levels are set per SVC.
Namely, when setting an SVC with the SETUP message, each of the ATM communication nodes can set the priority levels per SVC in a connection/priority level table.
As a result, each of the ATM communication nodes can make reference to the connection/priority table to easily recognize the priority levels of the connection.